This invention relates to the method and apparatus for cleaning pipe, and more particularly to such a method and apparatus for cleaning the outside of the pipe as the apparatus moves along the pipe.
Heretofore, self propelled apparatus has been provided, such as shown in U.S. Pat. No. 4,603,516 for cleaning the outside of pipe as the apparatus moves along a pipeline while supported thereon. Cleaning the outside of pipe removes loose rust, scale and dirt, to prepare the pipe for the subsequent application of a coating material on the outer surface of the pipe to minimize corrosion and prolong the service life of the pipe. In some instances, the pipe may be wrapped with an outer lining material containing an inner coating material for contacting the outer cleaned surface of the pipe. Normally abrasive particles, such as hard shot particles or grit, have been thrown by centrifugal force from an impeller wheel or the like against the outside of the pipe for cleaning the pipe. Particularly where hard shot particles of a uniform size were used previously, a relatively smooth clean outer surface of pipe was provided.
It is desirable to have a roughness on the outer surface of the pipe to provide a strong bond between the pipe and coating. The roughness increases the surface area of the pipe in contact with the coating for "anchoring" the coating on the pipe. Such an increased area bond is particularly needed upon an expansion of the pipe resulting from pressure or temperature increases to maintain the bonding contact between the pipe and coating. The greater the roughness, the stronger the bond between the pipe and coating particularly for shearing stresses. An enclosed blast chamber or housing on a self propelled carriage travelling along the pipe has been utilized previously but such carriages have been relatively complex for carrying blast wheels or impellers and for assembly on and disassembly off the pipe.
Oftentimes, a pipe coating removal device utilizing high pressure water is provided ahead of the so-called de-scaling apparatus so that the pipe coating, such as a bituminous layer, is first removed before the de-scaling operation by a separate cleaning device. For example, as shown in U.S. Pat. No. 4,552,594 dated Nov. 12, 1985, a carriage travelling along a pipeline discharges high pressure water from water jets or nozzles for removal of an outer coating on the pipe. The nozzles are positioned about the pipe for oscillation as the apparatus moves along the pipe thereby to clean the entire outer periphery of the pipe.
An enclosed chamber or housing is normally provided on a travelling carriage of the pipe cleaning apparatus for maintaining the discharge water or grit in an enclosed volume about the pipe. However, the carriages heretofore for supporting the discharge nozzle and the assembly on and disassembly off the pipe have been relatively complex.
It is noted that in some instances a non-uniform cleaning of the pipe has been obtained as the distance of the nozzle to the periphery of the pipe varies substantially throughout the oscillation of the nozzle. Thus, a substantially reduced velocity is obtained at the ends of the arcuate stroke as compared with the center of the stroke.